I take it that you think that nearly all of the value of schooling is signaling? I used to take that view too, but the accumulation of evidence that I've seen leads me to believe that isn't the case.
For one thing I find it very hard to believe that we would waste so many resources on a nearly unproductive enterprise. There are plenty of entrepreneurs out there trying to make money by selling cheaper, in time and money, versions of education and they aren't very successful. Mainstream schools have experimented with programmed learning, lectures on video, self-paced learning, etc. and none of the methods have caught on. Why wouldn't they if they worked?
Of course its hard to believe that reading novels and poems contributes much to ones productivity on the job. So how do I square curriculum content with my view that education is productive? Here goes:
1. Education isn't mainly about learning specific subject matter. Rather education is mainly about practicing the sort of self-discipline that is necessary to be productive in a modern work environment. High school allows you to practice showing up on time and doing what you are told. College allows you to practice and work out techniques that work for you that allow you to take on and complete on time complicated multi-part tasks in an environment where you have considerable freedom about how you spend your time. Some people may be more talented than others at this sort of thing (you come to mind as someone who is particularly talented at self-discipline), but this is also an acquired skill that one can develop with practice, and everyone needs to develop certain work habits that make one more productive at both types of tasks.
2. Education is a consumption good. This should be self explanatory. At the margin school may be work, but infra-marginally at least some (if not most) people actually enjoy the reading, the lectures, the homework, etc.
3. Education is not just investment in work capital, its also an investment in consumption capital and social capital. I feel much more at home in the world due to the fact I understand certain cultural references. For example I know what someone means when they refer to someone else as a Prufrock. I also understand what someone is saying about a character in a music video if their costume invokes the evil robot Maria from Metropolis. I learned those things in college. The shared culture produced by the education experience expands our common language with a lot of meaning, and that produces huge network externalities. Knowing history does help me do my job, but it is much more important that it allows me to make analogies that will be understood by acquaintances. What good does it do to talk about Vietnam Syndrome with those who didn't live through that era if they don't know anything about the Vietnam war and its effects on our politics? What good does it do to denigrate McCarthyism if people don't know what that is? Obviously this list could go on and on. "The original position," "fair game," "zero-sum game," "categorical imperative" etc. etc. All very commonly used expressions whose meanings would probably be completely lost on someone who had three years of trade school after grade school and then went straight to work. But anyone who attended college has probably been exposed to those ideas through conversation if not through attending classes.
4. Some classes are very very valuable at work. Reading, writing and numeracy are all obviously important. Most people may learn those things in grade school, but a lot of people are still advancing in HS. If you do powerpoint presentations for English you are learning skills you may very well use later on the job. Math courses have big returns even controlling for IQ (I believe) and that would seem to indicate that they have value preparing people for a wide range of work. Its not just engineers who use math on the job these days. Many blue collar workers are programming numerically controlled machine tools and have to understand statistical quality control.
In short, I think you are way off track on your thinking on education. -- Bill